Controlled release formation for urea

ABSTRACT

A hydrolyzed lignosulfonate-acrylonitrile graft copolymer matrix providing slow release solubility to urea fertilizer. The hydrolysis of the graft copolymer of lignosulfonate and acrylonitrile may be carried out in the presence of a caustic in situ during the urea prill manufacturing process or in a prehydrolysis step with subsequent use of the hydrolyzed copolymer in the urea prill manufacturing process to provide the controlled release formulation for urea.

BACKGROUND OF THE INVENTION

The present invention relates to urea fertilizers, and more particularlyto a controlled release formulation for urea fertilizers.

Fertilizers are generally classified into two major groupings, namely,natural organic products and synthetic chemical products. Syntheticchemical product examples would be urea, ammonia phosphates, and manyothers. Natural organic products are typically by-products fromprocessing of animal or vegetable substances that contain plantnutrients of value as fertilizers. Currently, the three principal typesof commercialized natural organic materials are activated sewage sludge,co-polymerized leather tankage, and hydrolyzed leather meal. Sludge istypically filtered off from an aeration reactor and heat dried forcommercial use as a slowly soluble nitrogen source available throughmicrobial degradation. However, because of its low nutrient value sludgeis generally used only as a base for fertilizers sold particularly tothe home and garden market. Various materials containing unavailablenitrogen as keratin are used to make process tankage. The principalcommercial products are manufactured from leather scrap by treatmentwith steam under pressure. This treatment hydrolyzes the keratin topurines and amino acids which are more available nitrogen sources. Aco-polymer of leather tankage and methylene urea is also available.

Controlled release fertilizers include natural organic and syntheticchemical products in which the release or availability of plantnutrients is in some way deliberately regulated so as to distribute thenutrient uptake over time. Controlled nutrient uptake can be achievedeither through modification of the fertilizer product itself, e.g.reduced solubility, coating, or encapsulation, or through regulation ofnutrient availability by the plant, e.g. nitrification inhibitors. Ingeneral, controlled release fertilizers have the following advantagesover natural organic sources. First, controlled release fertilizersprovide a reduction in the nutrient losses that occur betweenapplication and uptake by the plant. Secondly, controlled releasefertilizers provide for the reduction of nitrogen toxicity, particularlyto seedlings, caused by high ionic concentrations associated with rapiddissolution of soluble organic fertilizers or from the evolution ofammonia by hydrolysis of urea salts. Finally, controlled releasefertilizers provide a reduction in the number of fertilizer applicationsnecessary thus resulting in substantial cost savings.

The above advantages are particularly advantageous with respect tonitrogen sources for plants because more avenues of nitrogen loss existthan for phosphorous and potassium. For example, denitrification ofanhydrous ammonia can cause volatilization losses of ammonia, andnitrogen may be removed from the root zones of plants because ofleeching or other movement of these nutrients in the soil. This loss isa particular problem in porous or sandy soils, soil subject to heavyrainfall, soils with substantial ground water movement and runoff, andareas that are heavily irrigated. Also, nitrogen may become unavailableto the plant if it forms an insoluable compound in the soil.

The most common method of modifying the fertilizer product itself toprovide controlled nutrient release is to control the solubility of thefertilizer. In the case of urea, such products are typically made byreacting the urea with various aldehydes to reduce the solubility of thematerial. For example, isobutylidene diurea (IBDU), as described in U.S.Pat. No. 3,322,528, is a condensation product of urea andisobutyraldehyde which contains about 31% nitrogen of which 90% is waterinsoluble. The rate of nitrogen release is a function of soil moistureand the size of the IBDU particle so that the more moisture availableand the finer the particle size, the more rapid the rate of nitrogenrelease.

Urea has also been reacted with formaldehyde and consists mainly ofmethylene urea polymers varying in chain length and degree of crosslinking. Nitrogen is released from the insoluble portion of thesematerials by microbial degradation and therefore factors such as soilmoisture, temperature, pH, nutrient content and oxygen which influencethe rate of microbial activity also effect the rate of nitrogen release.As with the production of IBDU, the urea actually takes part in thereaction to form urea formaldehydes.

Modification of the fertilizer product to control the amount of nutrientuptake can also be achieved by coating soluble fertilizers to meter thenitrogen release. Coatings are generally classified into one of threetypes. First, there are semipermeable membranes which are broken down byinternal osmotic water pressure built-up by vapor diffusion. Release ofthe nitrogen from the soluble fertilizer is usually complete once thecoating is broken. Another type of coating involves the use ofimpermeable membranes with small pores. In this type of coating waterpasses through the coating and dissolves the fertilizer, causingswelling of the capsule and enlargement of the pores. The dissolvedfertilizer then diffuses through the enlarged pores in the coating.Finally, impermeable membranes without pores are utilized to coatsoluable fertilizers. In this type of coating, chemical, physical ormicrobial action degrades the membrane material before fertilizerrelease occurs, and nutrient release is usually complete once thecoating is degraded.

Several controlled release products are polymer coatings based onimpermeable membranes with small pores to coat prilled, solublefertilizers. Release of the nutrients can be varied by changing thethickness of the coating. The rate of release is also governed by soiltemperature i.e. higher temperatures increase the nutrient release rate.One such material is a fertilizer coated with a copolymer ofdicyclopentadiene with glycerol ester. Nutrient release varies with thethickness of the coating which ranges between 4% and 15% of the finishedproduct weight. Another type of polymer coated fertilizer consists ofcoated urea, ammoniated superphosphoric acid, and potassium chloride. Inthis case, the nutrients are released through microscopic pores in thecapsule wall which includes a low molecular weight polyethylene.

Sulfur coated urea has also been utilized to provide a controlledrelease fertilizer. Nitrogen release is based upon the thickness andcompleteness of the sulfur coating, the soil moisture, and the soiltemperature. Increased soil moisture and temperature accelerate thedegradation of the impermeable sulfur coating and thus the diffusion ofurea through the pores in the coating. For such products, the rate ofnitrogen release is expressed as a seven day dissolution rate. The sevenday dissolution rate is measured as the percentage of urea thatdissolves when a 50 gram sample of the product is immersed in 250 ml ofwater at 37.8° C. for seven days. Typically, these products have sevenday dissolution rates of between 25% and 35% which indicates a rapidinitial rate of nitrogen release.

As previously mentioned, controlled release of the fertilizer nutrientsmay also be accomplished through nitrification inhibitors. Nitrificationis the process which converts ammonium ions, when applied to the soil asammonium nitrogen, by bacterial oxidation to nitrate ions. Certainmaterials inhibit nitrification because they are toxic to the soilbacteria that oxidize ammonium ions. For example certain pesticides andchemicals such as nitropyrine and chlorinated pyridines are toxic to thebacteria that convert ammonium ions to nitrate. Thus, these types ofinhibitors delay conversion of ammonium nitrogen to nitrate byspecifically inhibiting the activity of the soil bacteria.

A controlled release mechanism can also be achieved by combining solublefertilizers with carriers such as glass, diatomaceous earth, waxes,parafins, polymers or resins. One of these products is based onformulating micronutrient ingredients with slowly soluble glass andfritted materials. These materials are made by mixing trace elements ofiron, zinc, manganese, copper, boron, or molybdenum with silicates,borates, or phosphates used to make glass. The mixture is thenhomogenized in a smelting process and the resultant solid mass isshattered and ground to the finished product.

Another product is based on mixing fertilizer ingredients with asuitable binder to produce a highly compacted product sold as a spike ortablet.

SUMMARY OF THE INVENTION

A hydrolyzed lignosulfonate-acrylonitrile copolymer matrix providingslow release solubility to urea.

The hydrolysis of the graft copolymer of lignosulfonate-acrylonitrilemay be carried out with caustic, such as lithium, potassium, or sodiumhydroxide, in situ directly in the urea prill manufacturing evaporationprocess or in a prehydrolysis step with subsequent use of the hydrolizedcopolymer with urea in the prill manufacturing process to provide theslow release formulation. In both cases, lignosulfonate is first graftcopolymerized with acrylonitrile in various loadings of 5 to 200% ofacrylonitrile with 30 to 60% preferred.

In the former case, the graft copolymer of lignosulfonate-acrylonitrileis treated with caustic, such as lithium, potassium or sodium hydroxideat 10 to 200% based on copolymer solids, with 30 to 60% preferred, andeither spray dried or used as a liquid. The causticized material is thenmixed with a urea solution and heated to about 285° F. to evaporate thewater in the urea solution. This in situ heating hydrolyzes thelignosulfonate-acylonitrile copolymer to a lignosulfonate-polyacrylicacid copolymer. The molten urea is then injected as droplets to an aircooling tower where crystalline urea is formed as a hard prill or beadof urea used for shipment. The hydrolized graph copolymer oflignosulfonate-polyacrylic acid is the matrix that protects the urea todecrease its solubility and provide a slow release formulation for aurea fertilizer.

In the latter case, a prehydrolyzed copolymer is formed for use in theprill manufacturing process by treating the graft copolymer with causticand hydrolyzing it at a desired temperature for a desired amount of timeto form the copolymer matrix of lignosulfonate-polyacrylic acid. Theprehydrolyzed copolymer is then neutralized to about 9.0 pH with anymineral acid such as sulfuric, phosphoric or nitric acid. This material,when added to urea at the desired solids concentration in water,preferably 70%, prior to water removal, and then the subsequent waterremoval therefrom in the prill manufacturing process will protect theurea from rapid solubility.

In either of the above two procedures, the graft copolymer loading onurea in the prill manufacturing process is about 2 to 20% with 5 to 10%preferred.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In preparing the controlled release formulation of the presentinvention, the first step is to prepare a graft copolymer oflignosulfonate with acrylonitrile. The acrylonitrile loading onlignosulfonate may be 5% to 200% with 30 to 60% preferred. 5% is thepractical lower limit at which the present invention begins to protecturea from solubility i.e. increases insolubility of urea from about 10to 20 times that of untreated urea. Likewise, 200% is the practicalupper limit since beyond 200% poor crystallization will occur due to theexcess acrylonitrile. Also, beyond this upper limit a poor matrix willform due to an insufficient amount of lignosulfonate present in thematrix.

Without wishing to be bound by any particular theory, it is thought thatthe graft copolymerization theory of a lignosulfonate with acrylonitrileentails classical, radical chain (addition) polymerization mechanisms.Initiation is carried out with a peroxide to form a free radicalterminus. The chain radical formed in the initiation step is capable ofadding successive monomers to propagate the chain. Propagation willcontinue until the supply of monomer is exhausted. However, classicaltermination reactions of the lignosulfonate require effective newinitiation of free radical sites throughout the reaction by peroxide.Also, chain transfer as well as retardation mechanisms may also bepresent.

As used herein, the term "Kraft lignin" has its normal connotation, andrefers to the substance which is typically recovered from alkalinepulping black liquors, such as are produced in the Kraft, soda and otherwell known alkaline pulping operations. The term "sulfonated lignin", asused in the specification, refers to the product which is obtained bythe introduction of sulfonic acid groups into the Kraft lignin molecule,as may be accomplished by reaction of the Kraft lignin with sulfite orbisulfite compounds, so that Kraft lignin is rendered soluble in water.As used herein, the term "sulfite lignin" refers to the reaction productof lignin which is inherently obtained during the sulfite pulping ofwood, and is a principle constituent of spent sulfite liquor. The term"lignosulfonate" (LSO₃) encompasses not only the sulfite lignin, butalso the sulfonated lignin herein above described. Any type oflignosulfonate i.e. hardwood, softwood, crude or pure may be employedduring the graft copolymerization step. Lignosulfonates are availablefrom numerous sources, such as from Reed Lignin, Inc. under the tradedesignation "Lignosol".

Acrylonitrile (AN) is a commonly available chemical having the chemicalformula CH₂ ═CHCN. Acrylonitrile may be prepared by the dehydration ofethylene cyanohydrin or acrylamide, and is available from numeroussources such as Aldrich Chemical Co. and Fisher Chemical Co.

Illustrative of the copolymerization of lignosulfonate withacrylonitrile is the following schematic reaction:

The following examples demonstrate the preparation of three differentgraft copolymers of lignosulfonate and acrylonitrile, i.e.polyacrylonitrile (PAN), in various loadings of acrylonitrile. It shouldbe noted that the ferrous sulfate heptahydrate is a catalyst utilizedalong with hydrogen peroxide to initiate free radicals for thepolymerization. Propagation of the chain is continued through the use ofhydrogen peroxide.

EXAMPLE 1

    ______________________________________                                                          Total Weight                                                                              Solids                                          Reactants         (grams)     (grams)                                         ______________________________________                                        Lignosol X (43.4%)                                                                              461             200                                         Water             400             --                                          Acrylonitrile (125 ml)                                                                          100             100                                         Ferrous Sulfate Heptahydrate                                                                    0.2             0.2                                         Total             1001.2  grams   300.2                                                                              grams                                  ______________________________________                                    

The above total weight chemicals were mixed and heated to refluxtemperature (70°-100° C.). 25% concentration hydrogen peroxide in waterwas added dropwise--1 ml. per 5 minutes for 3 hours and 35 minutes(total 43 mls.).

Excess acrylonitrile amounting to 5.8 mls. was distilled off forrecycle.

Recovered: 912 grams total weight, 277 grams solids, pH 5.2, Viscosityat 100 rpm Brookfield=12,960 cps, Viscosity at 20 rpm Brookfield=34,600cps.

EXAMPLE 2

    ______________________________________                                                          Total Weight                                                                              Solids                                          Reactants         (grams)     (grams)                                         ______________________________________                                        Hardwood Sugar Destroyed                                                                        200             100                                         SSL (Xyrofin 50%)                                                             Water             400             --                                          Acrylonitrile (125 mls.)                                                                        100             100                                         Ferrous Sulfate Heptahydrate                                                                    0.2             0.2                                         Total             700.2   grams   200.2                                                                              grams                                  ______________________________________                                    

The above total weight chemicals were mixed and heated to refluxtemperature (70°-96° C.). Hydrogen peroxide (25% concentration in water)was added dropwise (1 ml. per 5 minutes) for 3 hours and 50 minutes(total 46 mls.).

Excess acrylonitrile amounting to 1.6 mls. was distilled off forrecycle.

Recovered: 692 grams total weight at 28% solids,=194 gms. solids and pH4.7, Viscosity at 100 rpm Brookfield=305 cps, Viscosity at 20 rpmBrookfield=375 cps.

EXAMPLE 3

    ______________________________________                                                          Total Weight                                                                              Solids                                          Reactants         (grams)     (grams)                                         ______________________________________                                        Lignosol X (50%)  400             200                                         Water             440             --                                          Acrylonitrile (100 mls.)                                                                        80              80                                          Ferrous Sulfate Heptahydrate                                                                    0.2             0.2                                         Total             920.2   grams   280.2                                                                              grams                                  ______________________________________                                    

The above total weight chemicals were mixed and heated to refluxtemperature (69°-96° C.) and reacted while hydrogen peroxide initiator(25% concentration) was added dropwise (1 ml. per 5 minutes) for 2 hoursand 25 minutes (total 29 mls.).

Excess acrylonitrile amounting to 3.9 mls. was distilled off forrecycle.

Recovered: 878 grams at 31%=272 grams of solids, pH 5.2, Viscosity at100 rpm Brookfield=6240 cps, Viscosity at 20 rpm Brookfield=9000 cps.

Other examples are shown in Table I to illustrate the preparation of thegraft copolymer (PAN) of lignosulfonate and acrylonitrile.

                  TABLE I                                                         ______________________________________                                        LIGNOSULFONATE - PAN GRAFT COPOLYMERS                                         REACTION CONDITIONS                                                                  Acrylo-                Total                                           Raw    Nitrile, Time,   Temp.,                                                                              Solids                                                                              Final                                                                              Viscosity at                         Material                                                                             %        hrs.    C.    %     pH   20 rpm, cps                          ______________________________________                                        Lignosol X                                                                           50       3       96    30    5.2  34,000                               Lignosol                                                                             40       2       96    30    5.2  9,000                                Lignosol                                                                             40       2       96    30    5.4  14,800                               X                                                                             Lignosol                                                                             35       2       96    26    5.4  4,900                                X                                                                             Lignosol                                                                             25       2       96    30    5.6    20                                 X                                                                             Norlig A                                                                             50       5       96    30    3.7    250                                ______________________________________                                    

In a caustic environment, PAN graft copolymers prepared in the abovemanner may be hydrolyzed to give a graft copolymer of lignosulfonate andpolyacrylic acid (PAA) which thickens or insolubilizes depending uponthe graft copolymer loading of acrylonitrile. Hydrolysis may occur atroom temperature, but would take 1-2 days to complete. Therefore,hydrolysis is preferred to occur at elevated temperature where shorterperiods of time are needed to complete the process. For example,complete hydrolysis occurs, depending upon the acrylonitrile loading andthe caustic loading, if the causticized copolymer is heated at 90° C.for 0.5 to 3.0 hours. Also, as noted below, heating at 275° F. duringthe urea prill evaporation process sufficiently hydrolyzes thecopolymer. Thus, graft copolymers, such those as of Examples I-III, aretreated with caustic, such as lithium, potassium, or sodium hydroxide ata loading of 10 to 200% with 30 to 60% preferred based on caustic to PANcopolymer solids. The caustic loading is dictated by the amount ofacrylonitrile solids and a sufficient amount of caustic should be usedto hydrolyze all of the acrylonitrile. Use of an excess of caustic willmerely provide a high pH product which may be undesirable for certainapplications. This causticized product may then be spray dried or usedas a liquid during either of the following two preferred hydrolysissteps, i.e. (1) in situ during prill production or (2) in aprehydrolyzed system.

In present urea prill production, urea at 70% solids concentration inwater is heated in evaporators to about 285° F. to remove substantiallyall the water. The molten urea is then injected as droplets to an aircooling tower where crystalline urea is formed as a hard prill or beadof urea used for shipment. With the present process, 5% to 20% ofcausticized lignosulfonate acrylonitrile graft copolymer may be added tothe 70% urea solution prior to heating. The heating procedure forevaporation of the water at 285° F. is sufficient to hydrolyze the graftcopolymer of lignosulfonate and acrylonitrile (PAN) to a graft copolymerof lignosulfonate-polyacrylic acid (PAA). The causticized lignosulfonateacrylonitrile graft copolymer loading on urea is 2 to 20% with 5 to 10%preferred. With loading over 20% poor crystallization results, and withloading under 2% an insufficient matrix is formed which does not protectthe urea for a sufficient amount of time. The graft copolymer-causticsystem is soluble in molten urea and crystallizes with the urea whencooled. The hydrolyzed graft copolymer of lignosulfonate-polyacrylicacid is the matrix that protects urea from rapid dissolving and once themolten urea and hydrolyzed graft copolymer are crystallized it isbelieved that the hydrolyzed graft copolymer matrix serves to encase orentrap the urea providing slow release for the urea. Examples are shownin the screening method results herein where urea dissolving time hasbeen increased from one minute, 38 seconds to about 55 minutes.

As an alternative to the in situ graft copolymer-caustic systemdescribed above wherein hydrolysis occurs during the urea evaporationstep in the prill manufacturing process, a pre-hydrolyzed copolymer canalso be used with urea to obtain the insoluble matrix surrounding theurea to provide the slow release effect. In this case a graft copolymerof lignosulfonate and acrylonitrile, such as those in Examples I-III, istreated with caustic, such as lithium, potassium or sodium hydroxide andhydrolyzed independently of the urea evaporation step referred to above.Preferably, hydrolyzation occurs at 90° C. for approximately 0.5 to 3.0hours depending upon caustic and acrylonitrile loading, although anydesired temperature and time period may be employed. Hydrolysis of thecopolymer pendant nitrile groups occurs and a lignosulfonate-polyacrylicacid copolymer matrix is formed that may also be used to protect theurea from rapid solubility. The hydrolyzed graft copolymer is thenneutralized to about 9.0 pH with any mineral acid such as sulfuric,phosphoric or nitric acid. This material may then be spray dried forshipment or may be shipped in liquid form, and mixed with the 70% ureasolution prior to water removal. After evaporation of the water fromthis mixture at 285° F. this system is then cooled in the abovedescribed manner to form urea prill to provide the slow releaseformulation. In this pre-hydrolysis method, AN loading on LSO₃, causticloading, and PAA loading on urea is identical to that described abovefor the in situ hydrolysis process.

Illustrative of the hydrolysis of the graft copolymer LSO₃ -PAN is thefollowing schematic reaction: ##STR2##

The following procedure is utilized in obtaining the solubilityscreening referred to above and reported in Tables II and III:

1. Weigh 10 grams of urea.

2. Add graft copolymer caustic system or prehydrolized copolymer at thedesired loading based on urea.

3. Add water to a final urea concentration of 70%.

4. Distill water and heat the molten urea mixture to 285° F. in lessthan 5 minutes.

5. Cool rapidly to crystalize.

6. Break the crystalized mass and obtain a 0.4-0.45 gram solid piece.

7. Add the sample to 100 cc of water at 20°-25° C.

8. With intermittent swirling, measure the time to completely dissolvethe urea. Record as solubility index.

9. Measure the pH of a 3% solution and record.

The following test results have been obtained by utilizing the aboveprocedures. Table II represents test results utilizing thecopolymer-caustic in situ system and Table III represents resultsutilizing the prehydrolyzed system.

                  TABLE II                                                        ______________________________________                                        Graft Copolymer - Caustic In Situ System                                                       Treat-             3% Solu-                                                   ment,   Solubility tion                                                       % on    Index,     Final                                     Product          Urea    Mins. - Secs.                                                                            pH                                        ______________________________________                                        Control Urea     --       2 - 25    9.2                                       Evaporated to 285° F.                                                  Control Urea + 3.3% NaOH                                                                       --       1 - 38    9.9                                       Evaporated to 285° F.                                                  Desugared Hardwood SSL                                                                         10      55 - 0     9.1                                       100% PAN - 50% NaOH                                                           Desugared Hardwood SSL                                                                          5      30 - 0     9.6                                       100% PAN - 50% NaOH                                                           Lignosol X 50% PAN -                                                                           10      50 - 20    9.3                                       50% NaOH                                                                      Lignosol X 50% PAN -                                                                           10      32 - 20    9.7                                       50% NaOH - Powder                                                             Lignosol X 40% PAN -                                                                           10      17 - 35    9.4                                       30% NaOH                                                                      Lignosol X 40% PAN -                                                                           10      43 - 0     9.3                                       40% NaOH                                                                      Lignosol X 40% PAN -                                                                           10      47 - 0     9.2                                       50% NaOH                                                                      Lignosol X 40% PAN -                                                                           10      53 - 35    9.4                                       60% NaOH                                                                      ______________________________________                                    

                                      TABLE III                                   __________________________________________________________________________    GRAFT COPOLYMER PREHYDROLYSIS SYSTEM                                                                                       UREA PRILL PROCESS                                                COPOLYMER PROP.                                                                           (10% Loading on urea)                          REACTION CONDITIONS    VISCOSITY,                                                                            SOL. (1)                                                                             3% Final                                                                           Polymer                            SOLIDS,                                                                            NaOH,                                                                              TIME,                                                                             TEMP.,   20 rpm. INDEX  Test Test                 PRODUCT       %    %    hr. °C.                                                                         pH  cps     Min.' Sec."                                                                          pH   pH                   __________________________________________________________________________    40% PAN LX    20   50   1   90   12.8                                                                              26,000  56'                                                                              0"(L)                                                                             8.0  9.5                                10   40   3   90   12.9                                                                              1,300   57'                                                                              0"(L)                                                                             8.0  9.7                                                               60'                                                                              40"(P)                                                                            9.4  12.9                               20   20   3   90   12.0                                                                              93,000  40'                                                                              0"(L)                                                                             8.2  8.6                                20   10   3   90   10.4                                                                                45    26'                                                                              45"(L)                                                                            8.9  10.4                               10   30   3   90   12.8                                                                              2,100   55'                                                                              10"(P)                                                                            9.3  12.8                 35% PAN LX    10   40   3   90   12.9                                                                                100   52'                                                                              30"(P)                                                                            9.6  12.9                               10   30   3   90   12.7                                                                                174   63'                                                                              35"(P)                                                                            9.4  12.7                 UREA PRILL CONTROL                                                                          --   --   --  --   --  --      1  38" 9.9  --                   __________________________________________________________________________     (1) L = Liquid Hyd. sample tested.                                            P = Powder Hyd. sample tested.                                           

It is clear from the above Tables that urea insolubility has increaseddramatically when the matrix of the present invention is employedtherewith.

A slow release formulation has been described with comprises ahydrolyzed lignosulfonate-acrylonitrile graft copolymer matrix capableof giving slow release solubility to urea fertilizer. The hydrolysis ofthe graft copolymer lignosulfonate-acrylonitrile may be carried out insitu during the urea prill manufacturing process or in a prehydrolysisstep with subsequent use of the hydrolyzed copolymer with urea in theprill manufacturing process.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

I claim:
 1. A composition of matter, comprising urea and a hydrolyzedlignosulfonate-acrylonitrile copolymer matrix capable of providing slowrelease solubility for the urea wherein the loading of the hydrolyzedcopolymer to urea is about 2% to about 20% and the loading ofacrylonitrile to lignosulfonate in the copolymer is about 5% to about200%, and said copolymer matrix is hydrolyzed with a caustic selectedfrom the group consisting of lithium, potassium and sodium hydroxide,and wherein the loading of caustic to lignosulfoate-acrylonitrile isabout 10% to about 200%.
 2. The composition of claim 1, wherein theloading of acrylonitrile to lignosulfonate is about 30% to about 60%. 3.The composition of claim 1, wherein the loading of caustic tolignosulfonate-acrylonitrile is about 30% to about 60%.
 4. Thecomposition of claim 1, wherein said lignosulfonate is selected from thegroup consisting of a sulfite lignin, and a sulfonated lignin.
 5. In aurea fertilizer prill manufacturing process, a method of providing slowrelease for the urea fertilizer comprising the steps of:providing alignosulfonate-acrylonitrile copolymer having a loading of acrylonitrileto lignosulfonate in the copolymer of about 5% to about 200%;hydrolyzing the copolymer in caustic selected from the group consistingof lithium, potassium, and sodium hydroxide with the loading of causticto copolymer about 10% to about 200%; incorporating the hydrolyzedcopolymer in a urea solution with the loading of hydrolyzed copolymer tourea about 2% to about 20%; heating the urea solution and hydrolyzedcopolymer to evaporate water therefrom; and forming prill from thewater-evaporated urea and copolymer solution.
 6. The process of claim 5,wherein said lignosulfonate is selected from the group consisting of asulfite lignin and a sulfonated lignin.
 7. In a urea fertilizer prillmanufacturing process, a method of providing slow release for the ureafertilizer comprising the steps of:providing a urea solution containinga lignosulfonate-acrylonitrile copolymer and caustic selected from thegroup consisting of lithium, potassium and sodium hydroxide, and whereinthe loading of caustic to lignosulfonate-acrylonitrile is about 10% toabout 200% with the loading of acrylonitrile to lignosulfonate in thecopolymer about 5% to about 200% and the loading of hydrolyzed copolymerto urea about 2% to about 20%; heating the urea solution containing thecopolymer and caustic to simultaneously hydrolyze the copolymer andevaporate water therefrom; and forming prill from the water-evaporatedurea and copolymer solution.
 8. The process of claim 7, wherein saidlignosulfonate is selected from the group consisting of a sulfite ligninand a sulfonated lignin.